That is 3 sets of cylinders on those triplexes. They were failed experiments. It took multiple firemen to keep up with steam demand, mechanical stokers hadnít been invented yet. One engineer couldnít easily control basically 3 locomotives under one boiler. These huge mama-jamas were terrifically destructive to the track as well. These engines passed the limit of pre- super power steam technology and failed. And early diesels were only 10 years or so in the future.

Plans had been drawn by the Santa Fe for a quintplex around that time but articulated steam was basically done, except for maybe the N&W A clsss and the challengers/big boys of 20 years later...... but by then the diesel genie was already out of the bottle.